Various arrangements have been devised for a connectable and disconnectable fiber optic cable connector. One of the more significant problems of designing and building fiber optic cable connectors is that of maintaining adequate alignment at the light transmissive interface between the very small light carrying fibers of the typical fiber optic cables. To achieve good light transfer between fibers in an optical fiber connector, the two fibers must be accurately coaxially aligned. One method of obtaining this alignment, while protecting the fibers, is to contain the fibers in ferrules having matching diameters. The fibers are generally cemented or otherwise fastened in the ferrule so that they are concentric with the ferrule's outside diameter. After a cable has been secured in a ferrule, the ends of the optical fibers may be optically polished to enhance the percent of light transmitted between fibers.
The alignment of the ferrules with each other may be accomplished by insertion of the ferrules into a tube. If the tube is rigid some clearance must be designed into the parts, the amount of which depends on the precision of the parts. This clearance results in some misalignment of the small fibers causing coupling loss. However, if the sleeve is designed for interference fit with the ferrules, zero misalignment can be achieved with ferrules of the same diameter. For an interference fit, the sleeve must be resilient and the ferrules must be of slightly larger diameter than that of the sleeve.
At least one connector of this type has been manufactured using a plastic sleeve normally made of DELRIN. All plastics have a tendency to cold flow or creep to varying degrees, and the interference fit can become loose over time. Furthermore, plastics are dimensionally unstable with temperature variations as compared to metals. These instabilities defeat the purpose of an interference fit by introducing looseness between the ferrules and the sleeves resulting in fiber misalignment.
As illustrated in U.S. Pat. Nos. 4,205,898 and 4,193,665, alignment sleeves have been provided either with straight sides or with inwardly arcuate sides. These sleeves are, in general, mounted to an interconnect housing in a snug fit. One of the problems associated with a snug fit for the alignment sleeve is that connector bodies carrying ferrules must initially be accurately aligned with the sleeve. This requires the tolerances for the connector body and coupling apparatus to be exceedingly tight so as not to affect the axial alignment of opposing ferrules in the sleeve. Any tolerance errors in the coupling apparatus can provide forces transverse to the axis of the connector which can result in radial misalignment of the ferrules and thus the fibers contained therein.
Additionally, with flat sided or inwardly arcuate connector sleeve walls, contact with the ferrule is along relatively thin lines, thereby reducing the reliability of the overall connection system. Also, if flat-walled alignment sleeves are utilized, these sleeves are subject to fracture along the line of intersection between adjacent walls when ferrules are inserted into the sleeves.
Moreover, as will be appreciated, with flat-sided or inwardly arcuate walls, the sleeve must be substantially larger than the ferrule, which results in oversized interconnect housings since the housings must have inner diameters large enough to accommodate the relatively large sleeve.
By way of further background, U.S. Pat. No. 4,090,778 describes an optical fiber connector assembly which employs jewel-tipped ferrules in which the jewel diameter exceeds that of the cylindrical ferrule on which it is mounted. Oversided jewels are provided so that alignment of the fibers is made off the jewels rather than off the ferrules, e.g. from bearing surfaces established by the peripheries of the jewels vis-a-vis the ferrules. It will be appreciated that jewels, usually watch jewels, may be machined and manufactured to higher tolerances than a metal or plastic cylindrical member, with the hardness of the watch jewel providing an exceptionally stable alignment periphery.
One of the problems in utilizing the oversized jewel on an undersized cylindrical ferrule is that it is possible for the ferrules to cant or cock when inserted into an alignment sleeve.
Again, by way of further background, as illustrated in U.S. Pat. Nos. 4,140,366 and 4,140,367, an interconnect housing is provided in which an optical fiber is potted within the ferrule for providing structural rigidity and thus reliability. While potting is indeed desirable for connector reliability, it is oftentimes difficult and inconvenient to provide on-site potting.